1. Field of the Invention
The present invention relates to a halftone phase-shift mask which is used in a lithographic process in manufacturing a semiconductor device and also to a method of correcting a defect therein.
2. Description of Related Art
With an increase in the level of integration of semiconductor integrated circuits, there have been rapid advances in the minimizing of micropatterns used for circuitry. In lithographic technology used in a projection-type exposure apparatus, there is a limit to resolution that is caused by the wavelength of the light source used.
In recent years, to improve the resolution, there has been active development of phase-shift masks on which a pattern is formed on a photomask using a phase-shift material.
There has been a variety of types of phase-shift masks proposed to date, of which a halftone phase-shift mask that is disclosed in Japanese Unexamined Patent Publication No. 4-136854, which, because of its simple construction is starting to be used in production of semiconductor integrated circuits.
A description of the halftone phase-shift mask which is disclosed in Japanese Unexamined Patent Publication No. 4-136854 follows.
FIG. 18 is a drawing which illustrates the configuration of a halftone phase-shift mask that is disclosed in Japanese Unexamined Patent Publication No. 4-136854, FIG. 18 (a) being a cross-sectional view of the halftone phase-shift mask, FIG. 18 (b) showing the amplitude of light which passes through the halftone phase-shift mask which is shown in FIG. 18 (a), and FIG. 18 (c) being a drawing which shows the light intensity distribution on a wafer.
In the prior art, as shown in FIG. 18 (a), patterning is done of a translucent phase-shift film 1801 on top of a transparent substrate 1814 in a prescribed configuration.
In the case of radiating light onto a substrate such as shown in FIG. 18 (a), as shown in FIG. 18 (b), the light which passes through the translucent phase-shift film 1801, compared with the light that passes through the transmitted light pars 1808 at which the transparent substrate 1814 is exposed, has an attenuated amplitude and an inverted phase.
If this light is passed through a lens and projected upon the wafer, as shown in FIG. 18 (c), because of the phase inversion at the boundary between the transmitted light part 1808 and the translucent phase-shift film 1801, the light intensity at this boundary part is almost zero. For this reason, broadening of the light intensity distribution is suppressed, making it possible to transfer to a photoresist film a pattern having a high resolution.
The light which is transmitted through the translucent phase-shift film 1801 is not transferred to the photoresist film on the wafer with a single exposure only.
In the usual exposure process, however, the same pattern of one and the same photomask is transferred repeatedly at different positions on one and the same wafer. When doing this, rather than the entire photomask being transferred, only a part of the photomask is transferred by means of an aperture in the optics system of the projection-type exposure apparatus.
However, because it is difficult to perform precise exposure of only the transfer region at the aperture, when using a halftone phase-shift mask to perform repeated exposures, there are cases in which the transmitted light of the translucent part overlaps the boundary region, this being added to the amount of exposure light that is transferred.
To solve the above-noted problem, a halftone phase-shift mask in which the transfer region is surrounded by a light-blocking part was disclosed in the Japanese Unexamined Patent Publication No. 6-282063.
FIG. 19 is a top plan view which shows the configuration of a halftone phase-shift mask that is disclosed in the Japanese Unexamined Patent Publication No.6-282063.
In the prior art, as shown in FIG. 19, on the outside of the transfer region, an outer peripheral light block part 1902 that surrounds the transfer region is provided. This outer peripheral light block part may be a chromium film, for example, on an upper layer of the translucent phase-shift film 1901. By using this type of halftone phase-shift mask, it is possible to prevent unwanted transfer onto the transfer region.
A method for correcting a defect when it occurs in a halftone phase-shift mask is described below.
As shown in FIG. 19, there are four types of defects in the halftone phase-shift mask, a shifter residual part defect 1903, a shifter missing part defect 1904, a light block part residual part defect 1905, and a light-blocking part missing part defect 1906.
With respect to the shifter residual part defect 1903, a laser blowing method using a YAG laser that is used with photomasks in the past, or the method of using a focused ion beam (FIB) to perform gas-assisted etching can be used to correct the defect.
With respect to the light-blocking part missing part defect 1906, FIB assist gas deposition that uses either a hydrocarbon-based gas or metallic carbonyl gas that was generally used in the past can be used to bury a carbon type light-blocking film or metallic film to effect the correction of the defect.
With respect to the shifter missing part defect 1904, similar to the case of a light-blocking part missing part defect 1906, it is generally possible to use FIB assist gas deposition to bury a carbon type light-blocking film to correct the defect.
FIG. 20 is a plan view of a halftone phase-shift mask after correction of a shifter missing part defect 1904 as shown in FIG. 19.
As shown in FIG. 20, the shifter missing part defect 1904 is covered by a light-blocking part 1907, so that the shifter missing part defect 1904 is corrected.
Finally, with respect to a light-blocking part residual part defect 1905, there is currently no effect method of correction available. Because a light-blocking part residual part defect 1905 exists in the upper layer of the translucent phase-shift film 1901, methods which use laser blowing or FIB to remove the defect would also remove the translucent phase-shift film 1901.
As shown in FIG. 20, in the case in which a shifter missing part defect 1904 occurs near the light transmission part 1908, if the shifter missing part defect 1904 is corrected by covering the shifter missing part defect 1904 with the light-blocking part 1907, the light-blocking part 1907 after the correction exists near the light transmission part 1908, in which case, because there are different light transmission characteristics with respect to exposure light in the translucent phase-shift film 1901 and the light-blocking part 1907, a change occurs in the transferred photoresist pattern.
FIG. 21 is a top plan view which shows an example of a halftone phase-shift mask of the past that does not have a shifter missing part defect, and FIG. 22 is a drawing which shows a photoresist film transfer pattern for the case of using the halftone phase-shift mask that is shown in FIG. 21.
As shown in FIG. 21, in the case of performing exposure using a halftone phase-shift mask having a normal light transmission part 2108 and a translucent phase-shift film 2101 without a shifter missing part defect, the positive photoresist film after developing is as shown in FIG. 22, with a clean circular pattern 2210 formed in the photoresist film 2209.
FIG. 23 is a drawing which shows the photoresist film transfer pattern for the case of using the halftone phase-shift mask that is shown in FIG. 20.
As shown in FIG. 23, in the case of using a halftone phase-shift mask in which a shifter missing part defect 1904 was corrected as shown in FIG. 20, the positive phase-shift film 2309 after developing is the asymmetrical pattern 2312.
FIG. 24 is a graph which shows the light intensity distribution on the photoresist film for the case in which the halftone phase-shift masks shown in FIG. 20 and FIG. 21 are used. The solid line is the exposure light intensity on the photoresist film along the cross section C-C' shown in FIG. 20, and the dashed line is the exposure light intensity on the photoresist film along the cross section D-D' shown in FIG. 21.
In obtaining the above, a KrF excimer laser having a wavelength .lambda.=248 nm was used as the exposure light source, the numerical aperture (NA) of the projection lens system of the stepper used was 0.5, the coherence, .sigma., of the illumination optics system was 0.4, the projection magnification factor was 1/5, the size of the first light transmission section 8 was 1.25 .mu.m, and the light transmissivity T of the translucent phase-shift film 1 was 6%.
As shown in FIG. 24, in the case of using a normal halftone phase-shift mask without a defect, the light intensity distribution on the photoresist is symmetrical about the center, as shown by the dashed line.
However, when using a halftone phase-shift mask in which a defect has been corrected, the light intensity distribution on the photoresist is not symmetrical, as shown by the solid line.
This is because, in the halftone phase-shift mask in which a defect has been corrected, there is a light-blocking film 1907 that is formed in the region of the boundary between the light transmission part 1908 and the translucent phase shift film 1901, so that this part does not operate as a halftone phase-shift mask.
In the case in which a halftone phase-shift mask having such a corrected defect is used, for example, in forming a contact hole of a semiconductor circuit, variations occur in the electrical characteristics, this at times leading to failure caused by a short.
To solve the above-noted problem, a method of correcting a shifter missing part defect which uses a lift-off method was proposed in the Japanese Unexamined Patent Publication No. 7-146544.
FIG. 25 is a cross-sectional view which shows the configuration of a halftone phase-shift mask in which the defect correction method that is disclosed in the Japanese Unexamined Patent Publication No. 7-146544 has been applied.
In the disclosure made in the Japanese Unexamined Patent Publication No. 7-146544, as shown in FIG. 25, the lift-off method is used to bury in the shifter missing part defect 2504 a correction material 2517 of the same type as a translucent phase-shift film 2501.
However, to use the lift-off method, it is necessary to pattern the resist that is exposed only at the correction part, and there is a danger causing a new defect when performing patterning of the resist. Additionally, when using the lift-off method, there is the problem of a complex process of resist application, exposure, development, patterning, and resist peeling and the like being required, so that the correction time is long.
Additionally, to make the optical characteristics of the correction material by the lift-off method the same as those of the translucent phase-shift film 2501, it is necessary to perform exacting control of the sputtering conditions.
Another method of correcting a shifter missing part defect is disclosed in the Japanese Unexamined Patent Publication No. 7-219211.
FIG. 26 is a cross-sectional view which shows the configuration of a halftone phase-shift mask to which the defect correction method disclosed in the Japanese Unexamined Patent Publication No. 7-219211 has been applied.
In the method disclosed in the Japanese Unexamined Patent Publication No. 7-219211, as shown in FIG. 26, of the transparent substrate 2614, the bottom part of the shifter missing part defect 2604 is etched by using the FIB method, this causing a 180-degree shift in the phase, and beneath the etched region an ion-implanted layer 2618 is formed, thereby adjusting the transmissivity, so that this functions the same way as the halftone phase-shift mask.
However, because both the index of refraction and the absorption coefficient of the region in which ion implantation is done change, to impart the same optical characteristics to the ion-implanted region 1608 as the translucent phase-shift film 2601, it is necessary to control the etching depth and the amount of ion implantation.
Another method of correcting a shifter missing part defect is disclosed in the Japanese Unexamined Patent Publication No. 7-295204.
FIG. 27 is a top plan view of a halftone phase-shift mask to which the defect correction method which is disclosed in the Japanese Unexamined Patent Publication No. 7-295204 has been applied.
In the method which is disclosed in the Japanese Unexamined Patent Publication No. 7-295204, a shifter missing part defect 2704 is magnified by laser blowing, and the lift-off method which is the same as disclosed in the Japanese Unexamined Patent Publication No. 7-146544 is used to bury a correction material inside the magnified aperture part, after which laser blowing is used to form the actual aperture, thereby forming the corrected translucent phase-shift film 2721.
However, in the above method there is the same problem as occurs in the method which is disclosed in the Japanese Unexamined Patent Publication No. 7-146544, and there is an additional process that is required.
In a light-blocking part missing part defect, as shown in FIG. 19, if the defect occurs near the light transmission part 1908, similar to the shifter missing part defect after correction by means of the light transmission film shown in FIG. 20, there is a deterioration of the resist pattern transfer characteristics. With regard to this problem, it is not possible to use the past method of correcting a shifter missing part defect as is.
The present invention was made in consideration of the above-described drawbacks of the prior art and has as an object the provision of a method of correcting a shifter missing part defect and light-blocking residual defect of a halftone phase-shift mask without sacrificing the resist pattern transfer characteristics of the halftone phase-shift mask, and a halftone phase-shift mask to which this method is applied.